US2539465A

US2539465A - Television pulse and sound separator

Info

Publication number: US2539465A
Application number: US789057A
Authority: US
Inventors: Louis W Parker
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1947-12-01
Filing date: 1947-12-01
Publication date: 1951-01-30
Anticipated expiration: 1968-01-30
Also published as: FR975732A

Description

Jan. 30, 1951 l.. w. PARKER 2,539,465

TELEVISION PULSE AND SOUND SEPARATOR Filed nec. 1, 1947 IN V EN TOR.

BY Lau/s w. PARKER ATTORNEY Patented Jan. 30, 1951 Louis W. Parker, Little Neck, N. Y., assigner to International Standard Electric. Corporation, NewYork, N. Y., a corporation, cfg Delaware Application December 1, lfllhfsterial No79,l057 Claimst (Cl. M25-69.5)

rIjhe present` invention relates to a method of separating' the. various, synchronizing. 'iulss" 0f; a'composite` video signal, such as the line` and frame. 'Sindhfnizihe an@ C0161@ pulses?. from @1.1

another and' fromA the, accompanying intelligence signalssuchas picture andI sound signals, and'to @tre Ihffihqd? It `is customary in television systemsr tol transmitvthe various'synchronizing'signalsvin the form ofj'substantially rectangular pulses having amplitudes'greater'than the maximum amplitudes' of the picturensignals anddiifering from one an'-` other4 either inwid-th rV in amplitude, so as to`be separ'able'pat the receiver by means of"thresholdf devices or pulse width discriminators. vThe use of such vdevices makes it Anecessary to insurea ifirtually distortionless t-nansinis'sionf of the, 'synchroniz'ing llilses 'so'that 'they may bereadily separated without giving rise to false operatien'. A principal object of the present'invention is to provide a method ofdiire'rentiating between different types of syri'clji'ronizingI pulses where the pulses may be indistinguishable`irom one another with respect to' their width and/0r amplitude. Another object of the invention is`to provide a method ot diier'entiating between' pulses occurring at different but known intervals from one anothr- A further object of this invention is to provide a method of selecting from a set ofpulses 'oc` ourring at dii-ferent l'or random intervals onlythose pulses -tha'i'foccur with a predetermined cadence, or frequency of occurrence, and of sepl arately selecting further pulses bearing' a predetermined relationship with'the pulses thus olorained.

Still another object of the invention is to provide a novel arrangement 'at a television receiver f or discriminatingV between 'synchronizing pulses of different types;

Yet a further object of this invention is to provide at a television receiver, in combination with an arrangement for4 separating the synchronizing pulses from the intelligence signalsjmeans for i deriving from a synchronizing pulse' a blanking pulse occupying a predetermined time interval after the synchronizing pulse from which it has been derived.

A feature of the arrangement for discriminating between synchronizing pulses in accordance with the present nventionlis the small amount of operating power required", a preferred form of it comprising only a single vacuum tube in combination With a number of linear and non-linear effacement. fer sacrifie cui' this impedance elements including a plurality of small rectiers which may be of the crystal, cop.- per oxide or selenium type'.

The 'foregoing and other objects and features will become apparent in the course' of the follow.'- ing description, taken in'conjunction with the accompanying drawing the single figure of which shows'a discriminator circuit according to the invention.

The. circuit of the invention comprises a discriminator for selecting from an incoming Wave pulses of-V a certain minimum amplitude, a delay network to which the pulses are applied, said network having a time delay corresponding to, the intervals of the synchronizing pulses,

` means for combining the input and output of the'` delay network whereby the amplitude of. pulses occurring at the said intervals will be increased, and means for selecting the pulses of increased amplitude from any other pulses applied to the network.

The composite signal wave composed of synchronizing pulses mixedwith intelligence signals is appliedy at i to a pair of input terminals oney of which is grounded. In order to make the following description more readily understandable, it will be necessary to describe in some detail the make-up of the composite wave received at I. In the present instance it has been assumed that the receiver, of which the discriminator circuit illustrated forms a part, is designed for the re-Y production of color images at the rate of forty frames a second, each frame consisting ofthree color elds. Thus a vertical synchronizing impulse will occur times per second. The cadence of the horizontal synchronizing pulse train is assumed to be 31,250 pulses per second, that is to say. horizontal synchronizing pulses will occur at intervals of 32 microseconds. The horizontal scanning of successive color fields will be interlaced, i. e. the time position of the horizontal relative to the vertical synchronizing pulses will be displaced by half a horizontal interval, or 1 6 microseconds, during alternate elds. Accordingly, if the vertical synchronizing pulse is arranged to occur, upon completion of the scanning of an odd-numbered eld, at 8 microseconds after the next preceding horizontal synchronizing pulse, it will be seen that at the end of an evennumbered field the spacing between a horizontal and a vertical synchronizing pulse will be 24 microseconds. Similarly, if a color pulse is timed ninth, fifteenth, etc. field, the same type of pulse will occur 28 microseconds after the horizontal pulse at the end of the second, fourth, sixth, etc. frame which is after the sixth, twelvth, eighteenth, etc. field.

It will of course be appreciated that, if it were at all possible to adhere strictly to the above time schedules, the need for transmitting the various synchronizing signals would not arise since it would then be feasible to synchronize the receiver with impulses from local sources. The present invention, however, simply assumes that the actual signals will deviate but slightly from their predetermined timing, the amount of deviation being of the order of, say, one microsecond. It is also assumed that all synchronizing pulses have substantially the same amplitude (which is greater than the amplitude of all intelligence signals) and a constant width, for example one microsecond, but their precise shape is not critical.

The signal appearing at I is applied to the input of a vacuum tube 2 by way of a biasing circuit comprising a rectifier 3, a condenser and a resistor 5. The rectier 3 serves to build up a negative voltage on lthe right-hand plate of condenser 4 as the result of pulses applied to the left-hand plate thereof, the value of the resist'anc's 5 being selected so that the voltage on condenser Il will remain sufiiciently negative to insure that only the positive peaks of the pulses bring about the iiow of plate current in tube 2.

Connected between a source of anode potential andthe tube 2, which has been shown as a tetrode, is the primary of a transformer 6 having four secondaries designated 1, 8, 9 and Iii, respectively. The secondary 1 has one terminal Fgrounded and has the other terminal connected to a series resistor l i connected across the series combination of secondary 1 and resistor II is a delay network I2 shunted by a rectifier I3 which is in series with a source of fixed potential shown as a battery i4. The network I2 is composed of eight sections each designed to give a delay of 2 microseconds. The resistance I I is designed to provide a substantially refiection-free termination for the network i2 at the input end thereof; the value of this resistance in combination with the effective series resistance of the winding 1 is assumed to be small relative to the resistance to reverse current of rectifier I3: thus the voltage normally eifzisting across the input terminals of the network l2 will be substantially zero.

The pulses appearing across the secondaries 1, E, 9 and IB will be of such polarity that the upper terminals of these windings will be positive with respect to the associated lower terminals. Thus a positive voltage will appear across the network i2 whenevera pulse is passed by the tube 2 and applied to the transformer 6. The voltage of battery Il?. is selected to be appreciably greater than the amplitudes of these pulses so that rectifier i3 does not constitute a short circuit.

When a pulse is applied to the input of network I2 it travels to the end thereof in 16 microseconds, is reected and returns after a total interval of 32 microseconds to the input end of the network where it is substantially absorbed by the resistance il. If, at the time when the reflected pulse arrives at the resistance I I, a second pulse appears across the secondary 1, the amplitude of this latter pulse will be augmented by the amplitude of the reflected pulse and the voltage at the common terminal of resistor II and recter i3 will rise to almost double the amplitude of the original pulse. The lower end of secondary 8 is connected to this common terminal. The voltage of battery I@ is selected so as to place a definite limit upon the magnitude of the potential that may thus be applied to the secondary 8 of transformer 5.

The upper end of the secondary 8 is connected over a rectifier I to a time constant circuit which comprises a condenser it having associated therewith a shunt resistor i1 and a series resistor l. The amplitude of any randomly arriving pulse when measured across the resistances I1, It will be the sum of the voltages existing across the network I2 and across the secondary 8. This amplitude will reach a maximum whenever the incoming pulse coincides with the arrival of a pulse reflected from the end of network i2. Since it is assumed that horizontal synchronizing pulses will reach the transformer at 32 microsecond intervals, which is precisely the time required by a pulse for traveling to the end of the network. and back, there will appear across the network i6, I?, I8 a puise of maximum amplitude every time a horizontal synchronizing pulse appears at the input I (with the obvious exception of the rst pulse cf a series). These pulses of max-V imum amplitude build up a bias potential onv condenser i6 which, by virtue of a long time constant of elements IS, i1 somewhat in excess of' 32 microseconds, will prevent any random pulses The selected synchronizing pulses pass through the resistor i8 and develop a voltage drop thereacross which may be utilized, by means of a suitable lead connected to the upper terminal` of that resistor. to control the operation of the blocking oscillator (not shown) of the horizontal sweep generator associated with the receivers cathode ray tube.

vThe effect of the delay network l2 will be to place the synchronizing pulse upon a pedestal, thereby raising its amplitude suiciently to let the peak of the pulse pass through the rectifier I5 and the associated circuit. Since the peak portion of the pulse will be that part which appeared across the secondary 8, it will be of little importance if the pedestal, or the voltage appearing across the network I2, is somewhat distorted because of a widening of the original pulse during its passage through the network. Even a doubling of the original width of this pulse of l microsecond will not be critical.

It has been stated before that the vertical synchronizing pulse will occur alternately 8 and 24 microseconds after a horizontal synchronizing pulse. A connection between the lower end of secondary 9 and the mid-point of network I2 will pick up a pulse both 8 and 24 seconds after the occurrence of a horizontal synchronizing pulse. If another pulse, which will be a vertical synchronizing pulse, is impressed across secondary 9 at the same time, there will then appear a pulse of maximum amplitude across the network i5', I1', I8 connected in series with rectifier I5. The elements I5', I6', i1 and i8 have the same functions as their unprimed counterparts except that the time constant of the circuit I6', I1 has been adapted to the considerably lower rate of occurrence of the vertical synchronizing pulses which is pulses per second. The vertical synchronizing pulses may be utilized by means of a suitable lead connected to the upper terminal of` resis- In entirely analogous manner the color pulses may be obtained from the secondary I of trans.- former by means of a rectiel` I5 in series with a network consisting of a resistor I8 in series with the parallel combination of a resistor I'I" and a condenser I6. The lower end of winding I0 is connected to the I2 microsecond delay point on network i2 which is also the 20 microsecond delay point, the latter fact being however of no signiiicance. In accordance with the assumptions made before there will Yappear a pulse of maximum amplitude across the network I6, I'I", I8 in the third, ninth, fifteenth, etc. field or in any other frame while the pulses transmitted in the remaining frames. occurring 28 microseconds after the horizontal synchronizing pulse, will be lost; twenty color pulses per second however have been found to give an entirely satisfactory performance. The color pulses are picked up by means of a lead connected to the upper terminal of resistor I8 When the intelligence signals are to include sound as well as picture components then it is customary to place the sound signals at a definite time interval after the horizontal synchronizing pulse during the horizontal blanking period. The sound signals may comprise frequency modulated waves or time modulated pulses. In accordance with a further feature of the invention a blanking pulse, usable to cut off the beam of the kinescope and to unblock the sound demodulating equipment of the receiver, may be derived from the horizontal synchronizing pulse. The blanking pulse may have any desired width which in the present example has been fixed at four microseconds, The blanking pulse generator shown in the drawing comprises a delay network I9 having four sections, each designed to give a delay of 1 microsecond. At each l microsecond delay point there is provided a rectifier 2p connected in series with a common output circuit which comprises a resistor 2l in `series with the parallel comb-ination of a condenser 22 and a resistor 23. A iurther resistor 24 serves to terminate `the network i9 in its characteristic impedance, thereby preventing reiiections. The input o f network I9 is connected to the input of network I2 ovel` la 'resistance at serving, in combination with resistance II, to provide proper termination for the latter network.

Whenever a pulse is applied to the input of network iS, it will travel t0 the end of that network in four microseconds vand will be abSOrbed in resistance 2G, At -the zero, l, 2, 3 and i microsecond delay points, however, a small part 0f @he pulse energy will he taken oir through a respective rectifier 2i) and will be applied to the output circuit ZI, 22, 23 to produce a voltage drop across the resistor 2 I. Although theoretically composed of iive discrete pulse elements, the output of networl; .i9 will yactually represent a single pulse lasting four microseconds Ylonger than the horizontal synchronizing pulse, due to the distortion this pulse undergoes while passing ythrough the network.

The output circuit 2 I, ZZ, 2.3 will be recognized Thus the f i tial built up on condenser 22 also serves, however,

to provide a sharper cutoff at the end of the Afour* microsecond delay period. It may be noted that it is also possible to connect the network I 3 directly across the secondary 1, rather than across this winding in series with resistor II, in which case however there will be no discrimination be.- tween the different types of pulses applied to transformer 6 and pulses other than horizontal synchronizing pulses will also be followed by a blanking pulse. This however, need not cause any trouble even if each of these blanking pulses acts to unblock the sound demodulator, since sound modulation will be present only during the interval immediately following the line scanning pulse. With the arrangement shown in the drawing, however, blanking pulses will only be produced by horizontal synchronizing pulses properly identified by means of the network I2.

Although but -a single embodiment of the invention has been described and illustrated, it is to be understood that the invention is not limited to the precise arrangement shown andthat various modications and adaptations of the prin,- ciples herein disclosed will readily occur to those skilled in the art. In particular it Will be apparent that absolute and relative values different from those specified hereinabove may be employed without departing from the spirit and scope of the invention as deined in the yobjects and inthe appended claims.

What is caimed is:

l. In a television receiver, a discriminator for selecting synchronizing pulses, including horizontal lsynchronizing pulses occurring substantially at predetermined intervals and vertical synchronizing pulses occurring at a given point in an interval. between said horizontal synchronizing pulses, a single delay network common to all said synchronizing pulses and having a delay time corresponding to ,said predetermined intervals, means ior applying the received `horizontal and vertical synchronizing pulses to said common delay network, means for combiningthe input with the output of said delay network to increase the amplitude of horizontal synchronizing pulses occurring at said predetermined intervals, means coupled to said delay network at an intermediate delay point corresponding to the time position of said given point within lsaid intervals for picking up portions of the delayed pulses, means coupled to said pick up means for combining with increased amplitude the picked lup portions of said horizontal synchronizing pulses with subsequent vertical synchronizing pulses received at the time of said pick up, and means for selecting said pulses of increased amplitude from any other Vpulses applied to the network.

2. In a television receiver, a discriminator for separating different vtypes of synchronizing pulses, including a fi-rst type of pulses occurring substantially at predetermined intervals `and a second type of pulses each occurring substantially at a given point in an interval between pulses of the first type, comprising means for `receiving a composite signal wave, means for sefleeting vfrom said wave -puises oi certain mini mum amplitude, 5a single :delay network common to said different types of synchronizing pulses and having a delay time corresponding to said predetermined intervals, means for applying the selected pulses to the delay network, means for combining the input with the output of said delay network whereby the amplitude of pulses of the rst type occurring at said predetermined intervals will be increased, means connecting the output of said selecting means to an intermediate point on the delay network, the delay time on said intermediate point corresponding to 'the time interval between pulses of the nrst and second type, whereby the amplitude of pulses of the second type occurring at said given point within said intervals will be increased in amplitude by the delayed pulses of the first type, means for selecting from the input of the network the pulses of increased amplitude, and means for selecting from said intermediate point the pulses of increased amplitude.

3. In a television receiver according to claim 2 wherein said means for selecting pulses of increased amplitude each comprises a time constant circuit having a resistor in series with the parallel combination of a resistor and a condenser.

4. In a television receiver according to claim 1 comprising a second delay network having a delay time substantially less than the first delay network, means for applying said pulses of increased amplitude to the input of said second network, means interconnecting a plurality of delay points on said second network, and means for deriving a blanking pulse from said interconnecting means.

5. In a television receiver according to claim i wherein said interconnecting means comprises a plurality of rectiers.

6. In a television receiver according to claim 5 wherein each of said rectiers is connected in series with a time constant circuit comprising a resistor in series with the parallel combination of a resistor and a condenser.

7. A discriminator for separating horizontal and vertical synchronizing pulses from each other and from the rest of a television signai `wave comprising an amplier tube, means for applying said signal wave to the input of said tube, means for biasing said tube so as to pass current only upon the occurrence of pulses of predetermined amplitude, a transformer having its primary connected in the output circuit of said tube and having a plurality of secondaries, a single delay network commonto said horizontal and vertical synchronizing pulses and having a coeiiicient of reflection of substantially unity, means connecting the iirst of said seoondaries across the input end of said delay network, means for deriving a horizontal synchronizing pulse including another of said secondaries, means connecting one end of said other secondary to an input terminal of the delay network, a rectifier connected to the other end of said other secondary, and means for biasing said rectifier so as to pass only pulses of substantially maximum amplitude corresponding to the combination of a horizontal synchronizing pulse appearing across the rst and the second secondary with a delayed horizontal synchronizing pulse reflected simultaneously by the network, and means for deriving a vertical synchronizing pulse including a further one of said secondaries, means connecting one end of said further secondary to an intermediate point on said delay network, a rectifier. connected to the other end of said further secondary, and means for biasing said rectifier so as to pass only pulses of substantially maximum amplitude corresponding to the combination of a vertical synchronizing pulse appearing across the said'further secondary with a delayed horizontal synchronizing pulse existing simultaneously at said intermediate point.

8. A discriminator according to claim '7 wherein the input end of said network is terminated substantially in its characteristic impedance.

9. A discriminator according to claim '7 wherein said rectier biasing means each comprises a resistor in series with the parallel combination of a resistor and a condenser.

10. A discriminator according to claim 7 wherein said further secondary is connected to the midpoint of the delayl network.

1l. A discriminator according to claim '7, further comprising means for deriving a color synchronizing pulse including a fourth secondary of said transformer, means connecting one end of said fourth secondary to an additional intermediatepoint on said delay network, a rectifier connected to the other end of said fourth secondary, and means for biasing said rectifier so as to pass only pulses of substantially maximum amplitude corresponding to the combination of a color synchronizing pulse appearing across the said fourth secondary with a delay horizontal synchronizing pulse existing simultaneously at said additional intermediate point.

12. A discriminator according to claim 7, further comprising means for limiting the amplitude of a pulse appearing at the input end of the delay network.

13. A discriminator according to claim 7, further comprising a second delay network having a delay time substantially less than that of the rst delay network, means terminating said second network substantially in its characteristic impedance, means connecting the input end of said second network across the input of said first network, means interconnecting a plurality of delay points on said second network, and means for deriving a blanking pulse from said interconnecting means.

14. A discriminator according to claim 13 wherein said interconnecting means comprises a plurality of rectiiiers each connected between a respective delay point and an output circuit,

15. A discriminator according to claim 14 wherein said output circuit comprises means for biasing said rectiers so as to pass only pulses of substantially maximum amplitude, said biasing means including a resistor in series with the parallel combination of a resistor and a condenser.

LOUIS W. PARKER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,252,599 Lewis uAug. 12, 1941 2,309,506 Herbstl Jan. 26, 1943 2,416,424 Wilson Feb. 25, 1947